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An Engineer in Wonderland – Mosfet driver

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Have you ever had the feeling that you are the first person ever to want a certain building block?

There are a lot of different half-bridge mosfet drivers in the world, but almost all are designed to drive two n-mosfets.

This means that the top mosfet’s gate drive comes from a bootstrap circuit, which in turn means the half-bridge can never operate at 100% duty cycle.

I want 0-100% to build a bit of test gear, and so have been hunting for a half-bridge driver that will drive a p-channel mosfet at the top, and an n-channel below – at voltages from 4 to 20V, from a logic input.
 

The answer doesn’t even have to be combined p and n drivers as I have a microcontroller that can separately time the n and p control signals.

Note:

  • The Linear Tech LTC1693 (pictured) nearly perfect, but only works up to 13.2V.
  • The Nat Semi LM5111-4 is close, but tops out at 14V.
  • The Zetex ZXGD3002 works up to 20V, but needs an input signal up to Vcc.

Anyone know any chips, or a discrete circuit, that hits the spot?

Alice

Please respond below, or email alice@electronicsweekly.com

Tags: bootstrap circuit, bridge, first person, test gear, Wonderland

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2 Comments

  1. January 20, 2009 17:00

    The following might be a solution for your problem. Supertex has this very interesting isolated n-ch mosfet driver HT0440, which can be used up to 400V. It takes the power from the digital inputs. It doesn’t need any bootstraping or isolated power supply and it is relatively low cost. Downsides to the this IC, as can be expected, it can switch up to 100Hz at the most due to limited drive. But this may not be an issue if you are only doing switch on and off function once in a while. You will have to consider the gate capacitance of the mosfet because if it is too large the switching frequency will have to go down further.

  2. December 03, 2008 15:38

    I have the same problem, but it is worse for me as my requirement is a high side driver on a 28V automotive system and I need something that will stand at least 62V.
    Currently looking at the TLE6282G, it is a dual half bridge driver, but at least all the sections can be used independently. This chip uses bootstrap when switching and a charge pump for DC.
    Most bootstrap circuits can be made to work up to 99% DC.
    Regards, Jeremy